Hammer Screws & Skirting Board Fixings

What a hammer screw is

A hammer screw is a nylon plug with its screw already in it. You drill through the part you are fixing into the brick or concrete, push the plug through, and hammer the screw home: driving it in expands the plug against the sides of the hole. Mungo's fastening dictionary describes its nylon plugs (the MNA among them) this way: the expansion part is screwed or driven into the plug body, which locks it against the sides of the drilled hole. It is quick for repeat fixing along a wall because there is nothing to line up and screw in separately.

This page covers three fixings:

• •Mungo MNAF skirting board fixings: 5mm hammer screws with a PZ2 drive and a zinc plated screw, in dark brown, white or yellow so the head can be matched to the skirting or trim. Hobson lists them as skirting board fixings.
• •Mungo MNAR-Z hammer screws: a nylon plug with a cylindrical collar and an A2 (304) stainless steel screw, PZ2 drive, in 5, 6 and 8mm.
• •Wall screw, countersunk Torx: a zinc plated 7.5 x 70mm screw with an 11.5mm countersunk head (3.4mm high) and T30 drive that goes straight into a 6mm pre-drilled hole. Hobson lists it for concrete, hollow masonry and timber, for indoor applications, with small edge and spacing distances and low installation torque.
• •More Mungo hammer screws (MNA-G, MNA-S, MNA-Z and the MNAR-S) are on the nail in anchor page.

Which one for skirting boards, battens and trims?

Hobson publishes no load, pull-out or shear figure for any fixing on this page, so they are for light fixings that only have to hold the part itself in place. Do not use them for handrails, grab rails, shelving or cabinets that carry a load, anything overhead, or battens that carry ceilings, linings or cladding: those jobs need a fixing with published values, such as a concrete screw, sleeve anchor or chemical anchor, sized by the designer.

• •Skirting boards on brick or concrete walls: the MNAF skirting board fixing, in the colour that suits the board. Use the 30/5, 40/15 or 50/25 to suit the thickness of the skirting (see the size codes below).
• •Timber trims, light battens and fittings that only hold themselves, indoors: MNAF or MNAR-Z, picked by the thickness of the part.
• •Dry indoor work where you want a stainless screw rather than zinc: MNAR-Z, which has an A2 (304) stainless screw. Mungo calls for A4 (316) stainless in wet rooms (bathrooms, laundries), outdoors, in humid industrial areas and near the sea, and we list the MNAR-Z in A2 only, so ask us for an A4 fixing for those jobs.
• •A screw-in fixing into concrete, hollow masonry or timber, indoors: the 7.5 x 70 wall screw in a 6mm pre-drilled hole.

Hammer screw sizes and what 40/15 means

Mungo hammer screws are sold as diameter x length / usable length in mm. Mungo's dictionary calls the usable length tfix: the thickness of the part the screw fixes through. So a 5 x 40/15 is a 5mm hammer screw, 40mm long, for a part up to 15mm thick. Length minus tfix is the part that sits in the wall, and it is the same for every length of one diameter: 25mm for the 5mm screws, 30mm for 6mm and 40mm for 8mm. Plaster or render over the masonry counts as part of the fixture thickness, not the wall.

Hobson publishes no drill size or hole depth for the MNAF or MNAR-Z in the documents we hold. Check the pack, or ask us, before you drill. Select a row to open that fixing in the selector.

Drill size, loads, edge distance and spacing

Every fixing in masonry depends on how far it sits from an edge, how close it is to the next one and how thick and sound the wall is. For the fixings on this page, Hobson's documents give none of those figures, and no loads. Mungo's dictionary gives only general rules: consider the minimum edge distance to avoid failure of the building material, space fixings in a group 3 times the setting depth apart to reach their full load, and do not count plaster, flagstones or insulation as setting depth. That does not mean these fixings are unaffected by edges, thin walls or close spacing; it only means Hobson has not published the limits.

Zinc plated or stainless: indoors and outdoors

Mungo's dictionary says zinc coated steel fixings (5 micron zinc) are for indoor fixings, except wet rooms, and that outdoor work, wet rooms, humid industrial areas and sites close to the sea need A4 stainless steel (1.4401 or 1.4571, that is 316). Hobson's coatings chart likewise rates zinc plating as low corrosion resistance, for indoor and non-corrosive environments. So the zinc plated MNAF skirting fixings and the wall screw (which Hobson lists for indoor applications) are for dry indoor work.

The MNAR-Z has an A2 (304) stainless screw, and 304 is not the A4 grade Mungo calls for. So use the MNAR-Z indoors away from wet rooms, as Mungo allows for its zinc fixings. For wet rooms, anything outdoors (sheltered or not), humid industrial areas and sites near the sea, Mungo requires A4 (316) stainless, which we do not list in this range: ask us for an A4 fixing.

Mungo makes its nylon plugs from PA6, which it lists for temperatures from minus 40 to plus 100 degrees C.

How to fit a hammer screw

1. Pick the length: the usable length (the number after the slash) must be at least the thickness of the skirting, batten or trim, plus any plaster or render.
2. Hold the part in place and drill through it into the masonry at the drill size on the pack (Hobson's documents do not state it), deeper than the part of the fixing that goes into the wall. Mungo's dictionary matches the drilling to the wall: hammer drilling with SDS drills for concrete and natural stone, percussion drilling for solid brickwork, and rotary drilling without percussion for perforated brick and aerated concrete.
3. Blow the dust out of the hole.
4. Push the hammer screw through the part until the collar or head sits on it.
5. Hammer the screw home until the head is tight on the part.
6. For the wall screw: pre-drill 6mm, then drive the screw with a T30 bit, at low torque.

Hammer screws in Adelaide

Allmat supplies Mungo hammer screws, skirting board fixings, nail in anchors and masonry drill bits to carpenters, shopfitters, builders and trade across Adelaide and South Australia. Add them to a quote with your skirting, trims and the rest of your list, and we will price the lot.

Questions